Data synchronization method and system

ABSTRACT

The present invention discloses a data synchronization method and system. The method includes that: a first device adds a time stamp to a received data packet and transmits the data packet to a second device; the second device determines a transmission period to which the data packet belongs according to the time stamp of the data packet, and transmits data packets of different services which belong to the same transmission period by using air resources corresponding to the transmission period after the data packets of the different services which belong to the same transmission period are multiplexed. By the technical scheme of the present invention, air resources can be fully utilized.

TECHNICAL FIELD

The present invention relates to data communication technologies, andmore particularly to a data synchronization method and system.

BACKGROUND ART

With the development of communication technologies, a mobilecommunication system has been evolved into a System ArchitectureEvolution (SAE) system. The SAE system includes an Evolved UniversalTerrestrial Radio Access Network (E-UTRAN), and the E-UTRAN includes acore network and a wireless access network.

FIG. 1 is schematic diagram illustrating an E-UTRAN in a SAE system inthe prior art. As shown in FIG. 1, an evolved Node B (eNB) belongs tothe wireless access network, and the core network includes a MobilityManagement Entity (MME) and a Subscriber Gateway (S-GW). The eNB isadapted to provide a wireless interface for User Equipment (UE) such asa handset and so on. The MME is adapted to manage mobility contexts andsession contexts of the UE, and protect user information related tosecurity. The S-GW is adapted to provide functions of a subscriberplane. The MME and the S-GW may be in the same physical entity.Generally, the S-GW transmits user data streams through a GPRS TunnelingProtocol (GTP) to the eNB to which the UE belongs, and then the eNBtransmits the user data streams to the UE. Each eNB is connected withmultiple MMEs in an MME pool, and also is connected with multiple S-GWsin an S-GW pool. An interface between eNBs is called as an X2 interface,and an interface between the eNB and the MME or between the eNB and theS-GW is called as an S1 interface.

In order to effectively utilize air interface resources, some mobilecommunication services are provided to users in a broadcast andmulticast mode, and these mobile communication services are called asMultimedia Broadcast and Multicast Services (MBMS). Each MBMS isprovided in its own serving area, and in each cell of the serving area,a special control channel is used to transmit MBMS signallings. ABroadcast Multicast Service Center (BM-SC) is a multimedia broadcast andmulticast service providing center, MBMS data are transmitted from theBM-SC to the S-GW in a SAE network, then are transmitted to acorresponding eNB by the S-GW, and finally are transmitted to a user bythe eNB.

The MBMS service may be transmitted in a single carrier cell, and ifdifferent cells use different carriers, a user on the boundary of a cellonly receives the MBMS service of the current cell. If adjacent cellsuse the same carrier to transmit the same MBMS service, and transmit theMBMS service in a synchronization mode, the user on the boundaries ofthe adjacent cells can receive a signal obtained by overlapping energiesof the two MBMS services. Therefore, in the prior art, a continuous areais defined. In this area, all eNBs use the same carrier to synchronouslytransmit the same MBMS signal, to improve the receiving quality of theuser's MBMS service. The continuous area is called as a Single FrequencyNetwork (SFN) area.

The SFN area includes a group of cells which are continuousgeographically, and the cells use the same radio resources tosynchronously transmit a specific MBMS service. The SFN area exclusivelybelongs to one MBMS serving area.

FIG. 2 is a schematic diagram illustrating a conventional networkstructure by which an MBMS service is transmitted in a single carriercell. As shown in FIG. 2, a BM-SC is a provider of the MBMS service, andan MBMS-GW is a logic entity in a core network, e.g. an S-GW or a mixedentity of an S-GW and an MME. The BM-SC transmits MBMS data andsignaling to the MBMS-GW, and the MBMS-GW transmits the MBMS data toeNBs and transmits the signaling to an MBMS Control Entity (MCE). TheMCE is a control node, is adapted to configure radio resources of theeNBs, and transmits configuration signaling to each eNB. Dashedarrowheads in FIG. 2 represent the flow direction of signaling.

The performance can be improved obviously through synchronouslytransmitting MBMS data by all eNBs in the SFN area. At present,different technologies may be used to implement the data synchronizationtransmission between eNBs. In one technology, a network providessynchronization, i.e. a transmission network obtains synchronizationthrough clocks. In this technology, an IEEE1588 protocol may be used, tocoordinate clocks of all eNBs and make these clocks synchronous, and theaccuracy of these clocks is in a microsecond level. In anothertechnology, a synchronization signal is transmitted to each eNB througha common satellite signal, e.g. a Global Position System (GPS). Nomatter which technology is used, the object is to make all eNBssynchronously transmit signals, to implement the overlapping of signalsof different eNBs, thereby improving signal quality.

When MBMS data are transmitted from the BM-SC to each eNB, it ispossible that data packets are lost or lagged, so it is needed toprovide some mechanisms to guarantee that data transmitted by all eNBscan keep synchronous even if the data packets are lost or lagged.

A conventional mode includes that the BM-SC adds a synchronization framehead into a MBMS data packet, and the synchronization frame head mainlyincludes a time stamp and two counters. The time stamp is used toindicate absolution time in one synchronization period, one counter isused to indicate an Elapsed Octet Counter transmitted in onesynchronization period, and the other counter is used to indicate aPacket Number in one synchronization period. The two counters are set as0 at the beginning of each synchronization period.

MBMS data packets may be lost when being transmitted from the BM-SC tothe eNB, and the eNB determines how many data packets and bytes are lostduring the transmission procedure according to the Elapsed Octet Counterand the Packet Number in the synchronization frame head. The eNB needsto determine how many radio resources are occupied by the lost datapackets, and fills filling bits of which quantity is the same as thequantity of the lost data packets on the radio resources. A simpleexample is taken hereinafter to describe how the eNB calculates the lostdata.

For example, the eNB1 has received a first packet, the Packet Number ofthe first packet is equal to 1, and the Elapsed Octet Counter of thefirst packet is 50 bytes; the eNB1 receives a second packet again, thePacket Number of the second packet is 3, and the Elapsed Octet Counterof the second packet is 100 bytes; the eNB may determine that one packetis lost, the Packet Number of the lost packet is 2, and the ElapsedOctet Counter of the lost packet is 50 bytes; and thus the eNB1 needs toreserve air resources of 50 bytes on which any data can not betransmitted or predefined filling bits are transmitted. Another eNBxreceiving the packet of which Packet Number is 2 transmits the packetnormally. In this way, it can be guaranteed that the eNB 1 and the eNBxcan transmit the packet of which Packet Number is 3 by using the sameair resources.

The time stamp is used to indicate absolution time, to tell the eNB whendata are transmitted. According to a definition, the absolution timeindicated by the time stamp is multiples of 10 ms.

In the prior art, time stamps of data packets of the same service areidentical in each synchronization period of the BM-SC, and arecalculated according to time at which the BM-SC receives the first datapacket of the service in the synchronization period, a calculatingformula is as follows:

time stamp=time at which the BM-SC receives the first data packet+thelength of the synchronization period+a delay.

The delay relates to the largest transmission delay and a processingtime. The length of the synchronization period and the delay areconfigured by an operating and maintaining system. The change of thetime stamp means the start of a new synchronization period.

After receiving a data packet, the eNB determines, according to the timestamp, the time at which the data packet is transmitted. The eNB caches,multiplexes and transmits data in one transmission period, and this timeperiod is called as a MCH Subframe Allocation Pattern (MSAP) timeperiod. Generally, the length of the MSAP time period is the same as thelength of the synchronization period on the BM-SC, but on the eNB, thetime period is called as the MSAP time period or a transmission period.The MSAP time period corresponds to certain physical resources. Thephysical resources are composed of subframes with a certain format. Thesubframes do not need to be continuous in time, and the format is calledas MSAP. The eNB provides dispatching information to the UE, and thedispatching information relates to one MSAP time period. The dispatchinginformation is used to tell the UE which MBMS service is received onwhich subframe.

FIG. 3 is a schematic diagram illustrating an implementation in whichdata packets of the same service are transmitted in the samesynchronization period in the prior art. Suppose that the length of asynchronization period is 60 ms, the delay is 10 ms, and at 10: 00: 00:000, the BM-SC receives the first data packet of a service 1, called asa data packet 1 of the service 1, a time stamp added to the data packet1 by the BM-SC is 10: 00: 00: 000 (hour: minute: second:microsecond)+the length of the synchronization period+the delay=10: 00:00: 000+70 ms. After 10 ms, the BM-SC receives the second data packet ofthe service 1, called as a data packet 2 of the service 1, and the sametime stamp of 10: 00: 00: 000+70 ms is added to the data packet 2because the data packet 2 and the data packet 1 are transmitted in thesame synchronization period. The eNB has its own clock, and airresources corresponding to 10: 00: 00: 000+70 ms are a radio time slot1, so the data packet 1 of the service 1 should be transmitted at thetime corresponding to the radio time slot 1, and the data packet 2 ofthe service 1 should be transmitted following the data packet 1.

FIG. 4 is a schematic diagram illustrating an implementation in whichdata packets of different services are transmitted in the samesynchronization period in the prior art. Suppose that the length of asynchronization period is 60 ms, the delay is 10 ms, and at 10: 00: 00:000, the BM-SC receives a data packet 1 of a service 1, a time stampadded to the data packet 1 by the BM-SC is 10: 00: 00: 000+70 ms. After10 ms, the BM-SC receives a data packet 1 of a service 2, and a timestamp added to the data packet 1 of the service 2 is 10: 00: 00: 010+70ms=10: 00: 00: 000+80 ms. For the eNB, air resources corresponding to10: 00: 00: 000+70 ms are a radio time slot 1, so the data packet 1 ofthe service 1 should be transmitted at the time corresponding to theradio time slot 1; air resources corresponding to 10: 00: 00: 000+80 msare a radio time slot 2, so the data packet 1 of the service 2 should betransmitted at the time corresponding to the radio time slot 2.

DISCLOSURE OF INVENTION Technical Problem

If the data packet 1 of the service 1 is very large and the transmissionof the data packet 1 is not be completed in the radio time slot 1, thedata packet 1 of the service 2 can not be transmitted in the radio timeslot 2 and needs to be delayed. Vice verse, as shown in FIG. 5, if thedata packet 1 of the service 1 is very small and only a small amount ofdata are transmitted in the radio time slot 1, the air resources can notbe fully utilized, which results in waste. FIG. 5 is a schematic diagramillustrating another implementation in which data packets of differentservices are transmitted in the same synchronization period in the priorart.

The signaling transmission between the MCE and eNBs has the sameproblem. Referring to FIG. 2, since the MCE transmits control signalingto multiple eNBs and the multiple eNBs need to synchronously transmitthe control signaling, the transmission of the control signaling has thesame problem as the transmission of the service data.

Sum up, in the conventional data synchronization method, air resourcescan not be fully utilized.

Solution to Problem

The present invention provides a data synchronization method, in whichair resources can be fully utilized.

The present invention also provides a data synchronization system, inwhich air resources can be fully utilized.

In order to achieve the above object, technical schemes of the presentinvention are implemented as follows.

The present invention provides a data synchronization method, applied toa scene in which a first device transmits a received data packet tomultiple second devices, and the multiple second devices synchronouslytransmit a received same data packet, and the method includes:

adding, by the first device, a time stamp to the received data packet,and transmitting the data packet to the second device; and

determining, by the second device, a transmission period to which thedata packet belongs according to the time stamp of the data packet, andtransmitting data packets of different services which belong to a sametransmission period by using air resources corresponding to thetransmission period after the data packets of the different serviceswhich belong to the same transmission period are multiplexed.

The present invention provides a data synchronization system, whichincludes a first device and multiple second devices; the first devicetransmits a received data packet to multiple second devices, and themultiple second devices synchronously transmit a received same datapacket; where

the first device, adapted to add a time stamp to the received datapacket, and transmit the data packet to the second device; and

the second device, adapted to determine a transmission period to whichthe data packet belongs according to the time stamp of the data packet,and transmit data packets of different services which belong to a sametransmission period by using air resources corresponding to thetransmission period after the data packets of the different serviceswhich belong to the same transmission period are multiplexed.

Advantageous Effects of Invention

As can be seen from the above technical schemes that, in the presentinvention, the first device adds a time stamp to a received data packetand transmits the data packet to the second device; the second devicedetermines a transmission period to which the data packet belongsaccording to the time stamp of the data packet, and transmits datapackets of different services which belong to the same transmissionperiod on air resources corresponding to the transmission period afterthe data packets of the different services which belong to the sametransmission period are multiplexed. In this way, air resources can befully utilized.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is schematic diagram illustrating an E-UTRAN in a SAE system inthe prior art.

FIG. 2 is a schematic diagram illustrating a conventional networkstructure by which an MBMS service is transmitted in a single carriercell.

FIG. 3 is a schematic diagram illustrating an implementation in whichdata packets of the same service are transmitted in the samesynchronization period in the prior art.

FIG. 4 is a schematic diagram illustrating an implementation in whichdata packets of different services are transmitted in the samesynchronization period in the prior art.

FIG. 5 is a schematic diagram illustrating another implementation inwhich data packets of different services are transmitted in the samesynchronization period in the prior art.

FIG. 6 is a flowchart illustrating a data synchronization methodaccording to an embodiment of the present invention.

FIG. 7 is a schematic diagram illustrating data packet transmissionaccording to a first embodiment of the present invention.

FIG. 8 is a schematic diagram illustrating data packet transmissionaccording to a second embodiment of the present invention.

FIG. 9 is a schematic diagram illustrating data packet transmissionaccording to a fourth embodiment of the present invention.

FIG. 10 is a schematic diagram illustrating a data synchronizationsystem according to an embodiment of the present invention.

MODE FOR THE INVENTION

FIG. 6 is a flowchart illustrating a data synchronization methodaccording to an embodiment of the present invention. The method isapplied to a scene in which a first device transmits a received datapacket to multiple second devices, and the second devices synchronouslytransmit the same data packet. For example, in the scene mentioned inthe Background of the Invention, the BM-SC transmits the received MBMSservice data packet to multiple eNBs in the SFN, and the eNBs in the SFNsynchronously transmit the same MBMS service data packet. As shown inFIG. 6, the method includes:

Step 601: The first device adds a time stamp to a received data packet,and transmits the data packet to the second device.

Step 602: The second device determines a transmission period to whichthe data packet belongs according to the time stamp of the data packet,and transmits data packets of different services which belong to thesame transmission period by using air resources corresponding to thetransmission period after the data packets of the different serviceswhich belong to the same transmission period are multiplexed.

In this step, all second devices multiplex data packets in the sametransmission period by using the same predefined strategy.

By using the method shown in FIG. 6, the second devices can fullyutilize air resources to synchronously transmit the data packets.

In the method as shown in FIG. 6, the data packets transmitted from thefirst device to the second device may be lost, so a synchronizationframe head added into the data packets by the first device includes anElapsed Octet Counter and a Packet Number except a time stamp. In thisway, the second device may calculate the lost data packets according tothe Elapsed Octet Counter and the Packet Number, and reserve airresources for the lost data packets on which any data packet can not betransmitted or filling bits are transmitted. This implementation is thesame as that in the prior art, and will not be described in detail inthe embodiments of the present invention.

In the method as shown in FIG. 6, key technologies include that thefirst device adds which time stamp to the data packet, so that thesecond device can determine the transmission period to which the datapacket belongs according to the time stamp, which will be describedhereinafter in detail.

The following embodiments are described by taking an example of an MBMSservice scene, i.e. the BM-SC transmits received data packets tomultiple eNBs in the SFN, and the eNBs in the SFN need to synchronouslytransmit the same MBMS service data packet, to achieve an advantage ofcombining gains.

A First Embodiment

An operating and maintaining system configures parameters for a BM-SC,which include the length of a synchronization period, a serial number ofthe synchronization period and the start time of the synchronizationperiod. Similarly, an eNB also configures the length of a transmissionperiod, a serial number of the transmission period and the start time ofthe transmission period. Because of the largest transmission delay andthe largest processing delay from the BM-SC to the eNB, the start timeof the synchronization period on the BM-SC and the start time of thetransmission period on the eNB which have the same serial number aredifferent, and the start time of the transmission period on the eNB islagged for a period of time. For example, if the start time of asynchronization period with a serial number of 0 is 10:00:00:000 on theBM-SC, the start time of a transmission period with a serial number of 0is 10:00:00:650 on the eNB, and is lagged for 650 ms. Here, the laggedtime may be determined according to an actual transmission delay and aprocessing delay, or may be determined according to the length of thesynchronization period and a delay time. In this embodiment, the lengthand serial number range of the synchronization period on the BM-SC andthe length and serial number range of the transmission period on the eNBare preconfigured, the BM-SC and the eNB use the same configuration,when the synchronization/transmission period of the largest serialnumber comes, the serial number of the synchronization/transmissionperiod needs to be reconfigured as the serial number of the firstsynchronization/transmission period, circulated as such. For example, inthis embodiment, the length of the synchronization period is configuredas 640 ms on the BM-SC, and the serial number range of thesynchronization period is 0˜99; the length of the transmission period isconfigured as 640 ms on the eNB, and the serial number range of thetransmission period is 0˜99. The configuration of the time stamp and thetransmission of the data packets in this embodiment are shown in FIG. 7.

FIG. 7 is a schematic diagram illustrating data packet transmissionaccording to a first embodiment of the present invention. As shown inFIG. 7, a synchronization period 0 starts from absolution time 10: 00:00: 000, and the BM-SC receives the first data packet of a service 1 atthe absolution time 10: 00: 00: 000, called as a data packet 1 of theservice 1. A time stamp added to the data packet 1 of the service 1 bythe BM-SC is a serial number of the current synchronization period, i.e.a synchronization period 0. After 10 ms, the BM-SC receives the firstdata packet of a service 2, called as a data packet 1 of the service 2.Because the BM-SC receives the data packet 1 of the service 2 in thesynchronization period 0, a time stamp added to the data packet 1 of theservice 2 by the BM-SC is the synchronization period 0. In other words,in this embodiment, the BM-SC adds the same time stamp to all datapackets received in the same synchronization period, and the time stampis a serial number of the current synchronization period.

Referring to FIG. 7, when the eNB receives the data packet 1 of theservice 1 and the data packet 1 of the service 2, because the datapacket 1 of the service 1 and the data packet 1 of the service 2 havethe same time stamp, it is determined that the data packet 1 of theservice 1 and the data packet 1 of the service 2 need to be transmittedin the same transmission period with the serial number of 0. Of cause,the number of the data packets transmitted in the synchronization period0 by the BM-SC may exceed 2 shown in FIG. 7, so FIG. 7 only shows anexample. The eNB multiplexes all data packets in the transmission period0. For example, data packets of the service 1 which are belong to thetransmission period 0 are transmitted firstly, and then data packets ofthe service 2 which are belong to the transmission period 0 aretransmitted; or the data packets of the service 1 and the data packetsof the service 2 are transmitted by turns. For example, one data packetof the service 1 is transmitted firstly, and then one data packet of theservice 2 is transmitted; afterwards, another data packet of the service1 is transmitted, circulated as such. The eNB transmits the multiplexeddata on air resources corresponding to the transmission period 0.

In each embodiment of the present invention, the multiplexing strategiesof the eNBs in the same SFN are the same.

In order to shorten the length of the time stamp, in an embodiment ofthe present invention, the configuring method of the time stamp in theabove embodiment may be improved, i.e., the time stamp added by theBM-SC is the serial number of the synchronization period Mod adesignated value N (i.e. the serial number of the synchronization periodMod N). Here, N is any integer between 1 and a maximum serial number ofthe synchronization period.

For example, when N is equal to 2, the time stamp has two values 0 and1, so only one bit is needed to indicate the time stamp. When a certainservice starts, if the serial number of the first synchronization periodis 0, the BM-SC configures the time stamp of the first synchronizationperiod as 0 Mod 2=0, the time stamp of the second synchronization periodas 1 Mod 2=1, the time stamp of the third synchronization period as 2Mod 2=0, and the time stamp of the fourth synchronization period as 3Mod 2=1, circulated as such.

At the eNB, data of N transmission periods are stored. If N is equal to2, when receiving a data packet of the first synchronization period, theeNB configures a time stamp of the data packet as 0 and puts the timestamp in the first transmission period; when receiving a data packethaving a time stamp of 1, the eNB may learn that data of the secondtransmission period start. The eNB starts to transmit data packets ofthe first transmission period through an air interface. When receiving adata packet having the time stamp of 0 again, the eNB may learn thatdata of the second transmission period end. The eNB may start totransmit data packets of the second transmission period through the airinterface, circulated as such.

A Second Embodiment

An operating and maintaining system configures parameters for a BM-SC,which include the length of a synchronization period and a transmissiondelay. In this embodiment, the length of the synchronization period is640 ms, and the transmission delay is 10 ms.

The BM-SC adds the same time stamp to all data packets of the sameservice received in one synchronization period; or the BM-SC adds thesame time stamp to all data packets received in one synchronizationperiod, no matter whether the data packets belong to the same service.The time stamp is different from the serial number of thesynchronization period, but is absolution time.

If the BM-SC adds the same time stamp to all received data packets ofthe same service in one synchronization period, the time stamp added bythe BM-SC to data packets of a certain service received in onesynchronization period is represented by the following formula:

time stamp=absolution time at which the MB-SC receives the first datapacket of the service in the synchronization period+(or −) a fixedvalue.

If the BM-SC adds the same time stamp to all data packets received inone synchronization period, no matter whether the data packets belong tothe same service, the time stamp added by the BM-SC to the data packetsreceived in one synchronization period is represented by the followingformula:

time stamp=absolution time at which the MB-SC receives the first datapacket in the synchronization period+(or −) a fixed value;

or time stamp=absolution time at which the synchronization periodstarts+(or −) a fixed value;

the fixed value is 0, or the length of the synchronization period, orthe length of a delay time, or the length of the synchronization periodplus the length of the delay time.

If the time stamp is configured as absolution time at which thesynchronization period starts plus or minus a fixed value, the BM-SCneeds to configure the start time of the synchronization period, i.e.the BM-SC needs to learn the start time of each synchronization period.

FIG. 8 is a schematic diagram illustrating data packet transmissionaccording to a second embodiment of the present invention. Thisembodiment is described by taking an example that the BM-SC adds thesame time stamp to all data packets received in one synchronizationperiod, no matter whether the data packets belong to the same service,and the time stamp is absolution time at which the MB-SC receives thefirst data packet in the synchronization period plus the length of thesynchronization period and the length of the delay time. As shown inFIG. 8, a synchronization period x on the BM-SC starts from absolutiontime 10: 00: 00: 000, and at the absolution time 10: 00: 00: 000, theBM-SC receives the first data packet of a service 1, called as a datapacket 1 of the service 1. The time stamp added to the data packet 1 ofthe service 1 by the BM-SC is 0: 00: 00: 000+650 ms. After 10 ms, theBM-SC receives the first data packet of a service 2, called as a datapacket 1 of the service 2. Because the BM-SC receives the data packet 1of the service 2 in the synchronization period x, a time stamp added tothe data packet 1 of the service 2 by the BM-SC also is 0: 00: 00:000+650 ms.

Referring to FIG. 8, when the eNB receives the data packet 1 of theservice 1 and the data packet 1 of the service 2, because the datapacket 1 of the service 1 and the data packet 1 of the service 2 havethe same time stamp, it is determined that the data packet 1 of theservice 1 and the data packet 1 of the service 2 need to be transmittedin the same transmission period. The eNB makes the absolution time ofthe time stamp correspond to its own transmission period, for example,the time indicated by the time stamp is from 10: 00: 00: 640 to 10: 00:01: 280, which corresponds to the transmission period y of the eNB. Thetime stamp of the data packet 1 of the service 1 and the data packet 1of the service 2 is 10: 00: 00: 000+650 ms=10: 00: 00: 650, and is inthe range of the transmission period y, so the data packet 1 of theservice 1 and the data packet 1 of the service 2 are transmitted in thetransmission period y of the eNB. The eNB multiplexes all data packetsin the transmission period y, and transmits the multiplexed data on airresources corresponding to the transmission period y.

A Third Embodiment

An operating and maintaining system configures parameters for a BM-SC,which include the length of a synchronization period and a transmissiondelay. In this embodiment, the length of the synchronization period is640 ms, and the transmission delay is 10 ms.

In this embodiment, the BM-SC adds a time stamp to the first data packetof each service, does not add the time stamp to other data packets ofthe service, but needs to add an Elapsed Octet Counter and a PacketNumber to other data packets of the service. Here, the first data packetis the first data packet during the service, if the first data packetsof two services are received in the same synchronization period, theBM-SC adds the same time stamp to the first data packets of the twoservices. In this embodiment, the time stamp of the first data packetexclusively indicates a synchronization period in which the first datapacket is received, e.g. a serial number of the synchronization periodor absolution time by which the synchronization period can be deduced.The length of the synchronization period of the BM-SC is the same as thelength of the transmission period of the eNB, and if the time stamp is aserial number, the serial number range of the synchronization period isthe same as the serial number range of the transmission period.

Besides, the BM-SC needs to transmit a control frame which does notinclude service data to the eNB after data packets of each service inone synchronization period are transmitted, and the control frameincludes the number of the data packets of the service transmitted inthe synchronization period and the total byte number of the data packetsof the service transmitted in the synchronization period. If a certainservice has no data to be transmitted in one synchronization period, inthe control frame of the service corresponding to the synchronizationperiod, the number of the data packets of the service and the total bytenumber of the data packets of the service are configured as 0. In thisembodiment, in order to avoid that the eNB can not receive the controlframe, the BM-SC transmits the control frame for many times, e.g. 3times or 4 times.

The eNB determines a transmission period to which data packets of eachservice belong according to the time stamp of the first data packet ofthe service and the control frame of each synchronization period, andtransmits data packets of different services which belong to the sametransmission period on air resources corresponding to the transmissionperiod after the data packets of the different services which belong tothe same transmission period are multiplexed.

A Fourth Embodiment

An operating and maintaining system configures parameters for a BM-SC,which include the length of a synchronization period and a transmissiondelay. In this embodiment, the length of the synchronization period is640 ms, and the transmission delay is 10 ms.

In this embodiment, the BM-SC adds a time stamp to each received datapacket, and the time stamp is absolution time at which the data packetis received plus or minus a fixed value, i.e. the time stamp and theabsolution time at which the data packet is received have a linearityrelation.

The fixed value is 0, or the length of the synchronization period, orthe length of a delay time, or the length of the synchronization periodplus the length of the delay time.

When the fixed value is the length of the synchronization period plusthe length of the delay time, the method for adding the time stamp isthe same as the method for adding the time stamp in the prior art.

The eNB may map the received data packets into different transmissionperiods according an actual value of the time stamp.

FIG. 9 is a schematic diagram illustrating data packet transmissionaccording to a fourth embodiment of the present invention. Here, thisembodiment is described by taking an example that the fixed value is thelength of the synchronization period plus the length of the delay time.As shown in FIG. 9, a synchronization period x on the BM-SC starts fromabsolution time 10: 00: 00: 000, and at the absolution time 10: 00: 00:000, the BM-SC receives the first data packet of a service 1, called asa data packet 1 of the service 1. A time stamp added to the data packet1 of the service 1 by the BM-SC is 0: 00: 00: 000+650 ms. After 10 ms,the BM-SC receives the first data packet of a service 2, called as adata packet 1 of the service 2. A time stamp added to the data packet 1of the service 2 by the BM-SC also is 0: 00: 00: 000+650 ms.

Referring to FIG. 9, when receiving the data packet 1 of the service 1and the data packet 1 of the service 2, the eNB makes the absolutiontime indicated by the time stamp correspond to its own transmissionperiod. In this embodiment, the transmission period of the eNB is anMSAP time period, and the length and serial number range of the MSAPtime period may be the same as or different from the length and serialnumber range of the synchronization period of the BM-SC. For example, inthis embodiment, the length of the transmission period of the eNB is 640ms, a transmission period x of the eNB is from 10: 00: 00: 010 to 10:00: 00: 650, and the next transmission period y is from 10: 00: 00: 650to 10: 00: 01: 290. The time stamp of the data packet 1 of the service1, i.e. 10: 00: 00: 000+650 ms=10: 00: 00: 650, and the data packet 1 ofthe service 2, i.e. 10: 00: 00: 010+650 ms=10: 00: 00: 660, are in therange of the transmission period y, so the data packet 1 of the service1 and the data packet 1 of the service 2 are transmitted in thetransmission period y. The eNB multiplexes all data packets in thetransmission period y, and transmits the multiplexed data on airresources corresponding to the transmission period y.

In the above four embodiments, the present invention is described bytaking the synchronization transmission of MBMS service data in an MBMSservice scene as an example. However, it should be noted that thetechnical schemes of the above embodiments are applicable to thesynchronization transmission of control signaling between the MCE andthe eNB in the MBMS service scene. In the MBMS service scene, it is onlyneeded to replace the MB-SC in the above embodiments with the MCE, whichwill not be described in detail.

It also should be noted that in a scene in which control signaling issynchronously transmitted between the MCE and the eNB, the transmissionperiod of the control signaling on the eNB is generally called as amodification period. In the modification period, the control signalingmay be transmitted repeatedly to implement the transmission reliability.For example, control signaling 1 is transmitted for M times in amodification period corresponding to the control signaling 1, where M isany natural number. Before transmitting the control signaling 1, the MCEmay add synchronization information into the control signaling 1, andthe synchronization information indicates that the control signaling 1is transmitted in which modification period.

Universally, in the description of the embodiments of the presentinvention, the synchronization transmission period of the second device(e.g. the eNB in the above embodiments) is called as a transmissionperiod.

Based on the above embodiments, the present invention provides astructure of a data synchronization system.

FIG. 10 is a schematic diagram illustrating a data synchronizationsystem according to an embodiment of the present invention. As shown inFIG. 10, the system includes: a first device and multiple seconddevices. FIG. 10 shows three second devices, the first device transmitsa received data packet to multiple second devices, and the multiplesecond devices synchronously transmit the same data packet.

In FIG. 10, the first device is adapted to add a time stamp to thereceived data packet, and transmit the data packet to the second device;and the second device is adapted to determine a transmission period towhich the data packet belongs according to the time stamp of the datapacket, and transmit data packets of different services which belong tothe same transmission period by using air resources corresponding to thetransmission period after the data packets of the different serviceswhich belong to the same transmission period are multiplexed.

A method for adding the time stamp to the received data packet by thefirst device in FIG. 10 includes the following modes.

The first device is adapted to add the same time stamp to all datapackets received in the same synchronization period, and the time stampexclusively indicates the synchronization period; the same time stamp isa serial number of the synchronization period, or the serial number ofthe synchronization period Mod a designated value, where the designatedvalue is any integer between 1 and a maximum serial number of thesynchronization period, or absolution time at which the first devicereceives the first data packet in the synchronization period plus orminus a fixed value, or absolution time at which the synchronizationperiod starts plus or minus a fixed value; the fixed value is 0, or thelength of the synchronization period, or the length of a delay time, orthe length of the synchronization period plus the length of the delaytime.

Or, the first device is adapted to add a time stamp to all data packetsof the same service received in the same synchronization period, and thetime stamp exclusively indicates the synchronization period; for eachservice, the time stamp is absolution time at which the first devicereceives the first data packet of the service in the synchronizationperiod plus or minus a fixed value; the fixed value is 0, or the lengthof the synchronization period, or the length of a delay time, or thelength of the synchronization period plus the length of the delay time.

Or, the first device is adapted to add a time stamp to the first datapacket of each service, and not add the time stamp to other data packetsof the service, and the time stamp exclusively indicates thesynchronization period in which the first data packet is received; andadapted to add the same time stamp to the first data packets ofdifferent services if the data packets of the different services arereceived in the same synchronization period. For each service, the firstdevice is adapted to transmit a control frame to the second device afterdata packets of each service in each synchronization period aretransmitted, and the control frame comprises the number of the datapackets of the service transmitted in the synchronization period and thetotal byte number of the data packets of the service transmitted in thesynchronization period;

the second device, adapted to determine the transmission period to whichthe data packets of the service belong according to the time stamp ofthe first data packet of the service and the control frame of eachsynchronization period.

Or, the first device is adapted to add a time stamp to each receiveddata packet, and the time stamp is absolute time at which the firstdevice receives the data packet plus or minus a fixed value; the fixedvalue is 0, or the length of the synchronization period, or the lengthof a delay time, or the length of the synchronization period plus thelength of the delay time.

In FIG. 10, the first device is a multimedia BM-SC, and the seconddevice is an eNB. Of cause, there is an S-GW for forwarding data betweenthe BM-CS and the eNB.

Or, in FIG. 10, the first device is an MCE, and the second is an eNB.

Sum up, in the present invention, the first device adds a time stamp toa received data packet and transmits the data packet to the seconddevice; the second device determines a transmission period to which thedata packet belongs according to the time stamp of the data packet, andtransmits data packets of different services which belong to the sametransmission period by using air resources corresponding to thetransmission period after the data packets of different services whichbelong to the same transmission period are multiplexed. In this way, airresources can be fully utilized.

The foregoing are only preferred embodiments of the present inventionand are not for use in limiting the protection scope of the presentinvention. Any modification, equivalent replacement and improvement madewithin the spirit and principle of the present invention should becovered under the protection scope of the present invention.

1. A data synchronization method, applied to a scene in which a firstdevice transmits a received data packet to multiple second devices, andthe multiple second devices synchronously transmit a received same datapacket, the method comprising: adding, by the first device, a time stampto the received data packet, and transmitting the data packet to thesecond device; and determining, by the second device, a transmissionperiod to which the data packet belongs according to the time stamp ofthe data packet, and transmitting data packets of different serviceswhich belong to a same transmission period by using air resourcescorresponding to the transmission period after the data packets of thedifferent services which belong to the same transmission period aremultiplexed.
 2. The method of claim 1, wherein the adding, by the firstdevice, a time stamp to a received data packet comprises: adding, by thefirst device, a same time stamp to all data packets received in a samesynchronization period, and the time stamp exclusively indicates thesynchronization period; the same time stamp is a serial number of thesynchronization period, or the serial number of the synchronizationperiod Mod a designated value, where the designated value is an integerbetween 1 and a maximum serial number of the synchronization period, orabsolution time at which the first device receives the first data packetin the synchronization period plus or minus a fixed value, or absolutiontime at which the synchronization period starts plus or minus a fixedvalue; and the fixed value is 0, or the length of the synchronizationperiod, or the length of a delay time, or the length of thesynchronization period plus the length of the delay time.
 3. The methodof claim 1, wherein the adding, by the first device, a time stamp to areceived data packet comprises: adding, by the first device, a same timestamp to all data packets of a same service received in a samesynchronization period, and the time stamp exclusively indicates thesynchronization period; for each service, the time stamp is absolutiontime at which the first device receives the first data packet of theservice in the synchronization period plus or minus a fixed value; andthe fixed value is 0, or the length of the synchronization period, orthe length of a delay time, or the length of the synchronization periodplus the length of the delay time.
 4. The method of claim 1, wherein theadding, by the first device, a time stamp to a received data packetcomprises: adding, by the first device, a time stamp to the first datapacket of each service, and not adding the time stamp to other datapackets of the service, and the time stamp exclusively indicates asynchronization period in which the first data packet is received;adding a same time stamp to the first data packets of different servicesif the first data packets of the different services are received in asame synchronization period; the method further comprises: for eachservice, transmitting, by the first device, a control frame to thesecond device after data packets in each synchronization period aretransmitted, and the control frame comprises the number of the datapackets of the service transmitted in the synchronization period and thetotal byte number of the data packets of the service transmitted in thesynchronization period; and determining, by the second device, thetransmission period to which the data packets of the service belongaccording to the time stamp of the first data packet of the service andthe control frame of each synchronization period.
 5. The method of claim1, wherein the adding, by the first device, a time stamp to a receiveddata packet comprises: adding, by the first device, a time stamp to eachreceived data packet, and the time stamp is absolute time at which thefirst device receives the data packet plus or minus a fixed value; thefixed value is 0, or the length of the synchronization period, or thelength of a delay time, or the length of the synchronization period plusthe length of the delay time.
 6. The method of claim 1, wherein thefirst device is a multimedia Broadcast Multicast Service Center (BM-SC),and the second device is an evolved Node B (eNB); or the first device isa Multimedia Broadcast Multicast Service Control Entity (MCE), and thesecond device is an eNB.
 7. A data synchronization system, the systemcomprising: a first device and multiple second devices, wherein thefirst device transmits a received data packet to multiple seconddevices, and the multiple second devices synchronously transmit areceived same data packet; the first device, adapted to add a time stampto the received data packet, and transmit the data packet to the seconddevice; and the second device, adapted to determine a transmissionperiod to which the data packet belongs according to the time stamp ofthe data packet, and transmit data packets of different services whichbelong to a same transmission period by using air resourcescorresponding to the transmission period after the data packets of thedifferent services which belong to the same transmission period aremultiplexed.
 8. The system of claim 7, wherein the first device, adaptedto add a same time stamp to all data packets received in a samesynchronization period, and the time stamp exclusively indicates thesynchronization period; the same time stamp is a serial number of thesynchronization period, or the serial number of the synchronizationperiod Mod a designated value, where the designated value is an integerbetween 1 and a maximum serial number of the synchronization period, orabsolution time at which the first device receives the first data packetin the synchronization period plus or minus a fixed value, or absolutiontime at which the synchronization period starts plus or minus a fixedvalue; and the fixed value is 0, or the length of the synchronizationperiod, or the length of a delay time, or the length of thesynchronization period plus the length of the delay time.
 9. The systemof claim 7, wherein the first device, adapted to add a time stamp to alldata packets of a same service received in a same synchronizationperiod, and the time stamp exclusively indicates the synchronizationperiod; for each service, the time stamp is absolution time at which thefirst device receives the first data packet of the service in thesynchronization period plus or minus a fixed value; and the fixed valueis 0, or the length of the synchronization period, or the length of adelay time, or the length of the synchronization period plus the lengthof the delay time.
 10. The system of claim 7, wherein the first device,adapted to add a time stamp to the first data packet of each service,and not add the time stamp to other data packets of the service, thetime stamp exclusively indicates a synchronization period in which thefirst data packet is received; and adapted to add a same time stamp tothe first data packets of different services if the data packets of thedifferent services are received in a same synchronization period; thefirst device, adapted to transmit a control frame to the second deviceafter data packets of each service in each synchronization period aretransmitted, and the control frame comprises the number of the datapackets of the service transmitted in the synchronization period and thetotal byte number of the data packets of the service transmitted in thesynchronization period; and the second device, adapted to determine thetransmission period to which the data packets of the service belongaccording to the time stamp of the first data packet of the service andthe control frame of each synchronization period.
 11. The system ofclaim 7, wherein the first device, adapted to add a time stamp to eachreceived data packet, and the time stamp is absolute time at which thefirst device receives the data packet plus or minus a fixed value; andthe fixed value is 0, or the length of the synchronization period, orthe length of a delay time, or the length of the synchronization periodplus the length of the delay time.
 12. The system of claim 7, whereinthe first device is a multimedia Broadcast Multicast Service Center(BM-SC), and the second device is an evolved Node B (eNB); or the firstdevice is a Multimedia Broadcast Multicast Service Control Entity (MCE),and the second device is an eNB.